Manufacture of alkali carbonate or alkali hydroxide



Patented Oct. 30, 1934 UNITED STATES PATENT OFFICE Hermann 'Fricke and August Meier, Munich, Germany, assignors to Alterum Kredit-Aktien-Gesellschaft, Berlin,Germany, a company of Germany No Drawing. Application June 27, 1932, Serial No. 619,614. In Germany July 15, 1931.

3 Claims.

The invention relates to a modified process of manufacturing alkali carbonate or alkali hydroxide after the manner of the Leblanc soda process, with the recovery of ammonia as by- 5 product, in which alkali sulphate in admixture with carbon (or carboniferous material) is converted into alkali cyanide by the action of nitrogen at a high temperature, and the said alkali cyanide is hydrolyzedfor the manufacture of alkali carbonate or alkali hydroxide with the recovery of ammonia as a by-product.

According to the invention, the alkali sulphate carbon mixture is treated in known manner at an elevated temperature with steam and carbon dioxide and is then subjected to cyanization.

' As is known, by the treatment of alkali sulphate-carbon mixtures with steam and carbon dioxide at about 500 to 800 0., the alkali sulphate is converted into alkali carbonate, while the sulphur component is liberated in the form of sulphuretted hydrogen. As shown in experiments, theresult of this pre-treatment or transformation is that the conversion of the alkalicarbon mass into alkali cyanide is simple to carry out and is surprisingly good. Evidently, by the removal of sulphur which takes place in the pre-treatment, the mixture is brought into 'a state in which it affords, to the subsequent action of the nitrogen, excellent conditions for 30 the conversion into cyanide.

This satisfactory behaviour of the mixture is probably to be explained by the fact that, duringpre-treatment, the structure of the reaction mass becomes extremely porous and full of small passages and pipes. The chemical changes, for example for sodium sulphate, take placeaccording to the following known equations:

Therefore, during the removal of sulphur, there is a large proportion of gaseous substances which in part enter the reaction mass and in part escape therefrom. Since the mixture of alkali sulphate and carbon always contains both reaction substances in a finely divided form, it follows that the formation of a highly porous structure is necessarily a resultant phenomenon of the pre-treatment. Since, however, it is known that the form or state of an alkali-carbon mixture is an important factor in the action of nitrogen during the cyanization process, it may well be deduced from the surprisingly satisfactory results that the special structure formed in the mixture by the pre-treatment results in the surprising technical advantage which has beenfound.

As compared with the processes employed heretofore for the preparation of alkali cyanide from alkali sulphate, there is first of all the advantage that it is possible to carry out the new process without the addition of lime.

The most important advantage of the new process, however, resides more particularly in the fact that there is no necessity to purify the alkali product obtained by the steam-carbon dioxide treatment (carbonation), but that it is the impure product which is worked up further.

Further, an important advantage also residesin the fact that, due to its porous nature, the reaction mass permits considerably easier and better lixiviation after hydrolysis, than is the case with Leblanc crude soda.

The reaction mass may be employed with particular advantage in the briquetted form, thereby securing the advantage of a very compact charging of the individual constituents, in addition to that of a very effective porosity of the mass. In the experiments made it has been found that, generally, the briquettes possess '80 sufficient strength even without the addition of a binding agent.

In the experiments, cyanide was prepared in an amount of about of the theoretically possible quantity in a few hours at moderate 35 temperatures (850 to 950 C.) withoutthe use of any special catalyst and without, up to the present, any occasion to conduct the experiments in a manner, more exactly adapted to the substances employed. Thus it is possible to avoid the use of a catalyst such as iron, and in this Way avoid impurities in the finally obtained alkali occasioned by the presence of compounds of such catalyst.

Example I For the manufacture of sodium carbonate, 1,000 kilograms of sodium sulphate (of 98% purity) are mixed with 2,750 kilograms of brown coal (referred to the dry substance) and ground 100 to the fineness of powder. Due to the moisture of the brown coal and to special additions of water, the mixture has a moisture content of 16% of the total mass. The powdered mass is pressed to small briquettes and charged into a shaft furnace which is adapted to be heated.

After charging the shaft furnace, the mass is heated to about 900 0., the sulphate being thereby reduced to sulphide. When the reduction is completed, which is indicated by the fact no that no more 002 and CO gases are given off, the heating is so regulated that the furnace contents have a temperature of only 400 to 500 C.

At the lower temperature (4:00 to 500 C.) carbon dioxide and steam are passed through the mass of briquettes in order to convert the sodium sulphide into carbonate and to expel the sulphur as sulphuretted hydrogen, according to the equation:

The steam and carbon dioxideare preferably employed in excess. oeaerauy; er qeurseypee carbon dioxide obtained in'tlie' previoiis refine tion is also employed.

The mass is then heated again to a higher temperature and at the same nitrogen -is allowed to act upon the briquettes. rne aeeen of the nitrogen, which takes place at about 1,000 0., affects the conversion into sodium cyanide.- ,7 .7

After the cyanization is completed,- the mass iszsremoved fromthe furnace and istransferred toua container in which hydrolysis is carried out atabou teofl f C; During the action of the steam onithei cyanide, 190 kilograms of ammonia escape and are collectedin water in known manner.

After? hydrolysis, thecooled mass is introduced into a lixiviatingtank and=the soda is extracted byiwaterr- The solid residue and the liquor are separated; in known manner and the liquor is freed-iii. desired from any impurities it may contain; 690rk'ilograms of sodium carbonate of a purity of. 98% are recovered from the-liquor;

The solid residue" consisting of carbon and ash, istemployedefor heating purposes. The sulphnre'tted hydrogen formedby the action of carbon dioxide and steam onthe' sulphide is burnt in known manner; for the formation of sulphur; dioxide, which is then converted into sulphuric acid by the'contactprocess; 560' kilogramsrof sulphuric acid are thereby obtained-- The interaction ofithis sulphuric; acidwith the ammonia recovered in-the hydrolysis produces e 750==kilograms of'ammonium' sulphate;

Example II Briquettes of the" same raw material as 'in Example- 1 were subjected to the same treatment, as fares cyanizationjas in Example I.

Ther 'eupom-the reaction mass, broken up and spread put-in thin layerson shallow pans, was introduced into a hydrolysis container. Hy drolysis was then carried out=-by passing steam over 'the layers'at a temperature'of 'between 400 and 500- C.

In this hydrolysis, 166 kilograms of 'ammonia were rec'overedw The' reactionE mass contained 271 kilograms NaOI-I and 262"-"kilograins" of NazC'Oe. In addition, apart from traces of aluminate, silicate "andtlie like, the mass still contained about 10% of the introduced sulphate asalk ali sulphur compounds.

mixed with 1,850 kilograms of bituminous coal, are ground to the fineness of powder and are pressed to small briquettes.

The mass is then reduced by heating it in a shaftfurnace to about 900 C. and after completion of the reduction is carbonated at a temperature of 400-500 C. by carbon dioxide and steam.

Thereupon, the mass is again heated to a high temperature'of about"900 C. in a shaft furnace andsubjected to the action of nitrogen.

The reaction massis then broken up and Spreadout in thin layers on shallow pans and treatediatabout 4400 to 500 c. with steam, 139 kilograms of ammonia being thereby recovered. After this hydrolysis, the reaction mass contame; 325 kilograms of KOH and 275 kilograms of K2003; together with about 8% of the introduced sulphate as alkali sulphur compounds, and traces of aluminate, silicate and the like.

The; carbonate and hydroxide constituents of thd'reaction-mass are then separated and. purifi'ed in a known manner, and sent away as sale a-bl'e products,- while the alkali sulphur compounds are re-introduced into the process.

We claim:- A y ,7.

ve1. A process of manufacturin an alkali of the group including alkali metal carbonates and hydroxides; which comprises mixing and briguet ting the corresponding sulphate with carboniferous-material, heating to approximately900f C foreffecting a reductionto sulphide and the forming of pores in the briguettes by the evo: lution of gases formed in the reduction, heating to-between 400 and 500f C. while passing carbon dioxide and steamioreffecting a carbonation, heating ataproximately 900 to 1000 C. whilepassing nitrogen for effecting a cyaniza tion,- said heatings being accomplished in the substantial: absence of a catalyst and-, while maintaining the porous structure of the briquettes, thereafter hydrolyaing at approximately 400 0., and lixiviating the solid material with water whereby' to obtaina substantially pure alkalif free from compounds of the catalyst. 2. A; process of manufacturing an 'alkali of the group including alkali metal carbonatesand hydroxides, which comprises briouetting the corresponding. sulphate in admixture with carboniferous material, heating to approximately 900 to 1000 C.,for effecting areduction to sulphide and the"forming'ofporesin" the briquettes by evolution 'of'gases formed" in the "reduction; heating to between 400' and 500: C. whilepassing arben' dioxide and st'earnifor effecting: a v

carbonation, heating to approximately 900* while passing: mtregea for effecting'a cyani'z'a tion, said 'heating's being accomplished without removal of the material from the furnace whereby to avoidlossof' porosity, of'the mass and in the substantial absence of acatalystreactive withthe alkali to'be produ ed," thereafter hydrolyzing at approximately 460 0;, and, lixiviati'ng the sen 'nia en'er with ater whereby to obtain a atstariti ny urefamaurree ire or the catalyst, w erein the p s1 rrerritneeseaee erga s frfim the H v ing reduction is maintained through the pro-- Cesare and'availed of dul lixiv'iation for facilitati'ng me solution of "said" alkali.

3. A process of manuraeturing'an alkali metal hy roxide which comprises xin ana"- briboriirereue" material,j heating"ti approximately 900 o; for eifecting a'reduction tosiilp'hide compounds ture of the briquettes, thereafter hydrolyzing at approximately 400 C. in thin layers, and lixiviating the solid material with Water whereby to obtain the alkali metal hydroxide.

HERM. FRICKE. AUGUST LIEIER. 

